Blast vs. Consistency


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119er
December 7, 2012, 02:34 AM
Alright, gas operated .308 guns with 18" barrels. One AR10 clone and an M1A. H335 pushing a 147gr/150gr bullet. Let's discuss the former b/c it has no muzzle brake/flash hider to disguise muzzle blast.

At 42.0gr H335 there is noticeable blast/fireball at the muzzle. 41.5 does not have such blast and averaged 2567fps for five shots giving about 1.5" @100. Velocity @ 42.0gr was 2604fps.

Please realize that this is more a theoretical question than trying to make a match gun from a hunting rifle, but:

1.) Am I giving up any consistency due to pressure loading several grains below the maximum? (I know this assumes that the higher the pressure the better consistency which seems to be valid in most cases I've seen.)

2.) Is there anything to gain from dealing with muzzle blast vs. loading low enough to avoid it?

3.) I am familiar with loading for the M-1, but are there any ways to get into trouble with the open gas systems of the AR10(DI) and M1A(self regulating)?

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30Cal
December 7, 2012, 09:34 AM
Max loads typically don't deliver the best accuracy.

I shot an M1A with a muzzle compensator for a while and the blast was something to behold. Never bothered me (plugs + muffs), but everyone else complained. I shot 125's down at 2430fps for 200yds and don't think the blast really improved, (but I wasn't paying attention either).

The same stuff that holds for the M1 holds for the M1A. While the gas system is a little more tolerant, you can still crack the oprod or receiver if you beat on it.

bds
December 7, 2012, 11:33 AM
Here are some long-range match pet loads from The Rifleman's Journal - http://riflemansjournal.blogspot.com/2010/01/reloading-western-shooters-pet-loads.html


Palma match and other long-range match loads:
Brass: Winchester .308, weighs 170 gr., same as Lapua in capacity.
Powder: Varget, 46.0 gr.
Primer: Russian LR Magnum
Bullet: Berger 155.5 gr. Fullbore

Brass: Winchester .308
Powder: IMR 4895, 44.8 gr.
Primer: Federal 210M
Bullet: Sierra 155 (2155) 2.80" OAL

Brass: Lapua, approx. 170 gr. case weight
Powder: Varget, 46.6 gr.
Primer: Russian LR
Bullet: Berger 155.5 gr. Fullbore or Sierra 155 (2156)

Brass: WCC 60 or new Winchester (both weigh approx. 154 gr.)
Powder: H4895 44.5 gr.
Primer: Russian LR
Bullet: Berger 175 BT, moly-coated

Brass: Winchester, weight sorted
Powder: VV N150 46.5 gr.
Primer: CCI 200
Bullet: Berger 155.5 uncoated

Brass: Lapua, neck turned and weight sorted
Powder: 45.8 gr. of Varget
Primer: Russian LR Magnum
Bullet: Berger 155.5 gr. Fullbore

Brass: Lapua, weight sorted
Powder: 44.5 gr. of IMR 4320
Primer: Russian LR
Bullet: Berger 175 Grain Match Target BT

Brass: Lapua .308
Powder: N-150, 45.5 gr. .
Primers: Russian, Lot 1-03.
Bullet: Berger 155 VLD (naked)

Offfhand
December 7, 2012, 01:55 PM
It was interesting reading the "pet loads" in The Riflemans Journal mentioned in above post, especially the number of shooters who use the Audette measuring instrument to measure case variations. I'm guessing that they are no longer available. I have one that I never use and might consider selling it, wonder what it might be worth today? Anyone have any idea?

gamestalker
December 7, 2012, 05:50 PM
Compatable bullet weight / velocity with rate of barrel twist, barrel whip, harmonic distortion, and a host of other factors will usually degrade accuracy with full velocity loads to a greater degree, than loads worked up to that "sweet spot".

GS

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